Take Jenga and Clue; place Professor Plum on top of the Jenga tower. Play Clue normally, but every time a suggestion is made and disproved, pull a block from the Jenga tower and don't replace it. Solve the crime before the tower falls!
Actually in His Last Vow, Mycroft is listed as a previous agent---*unsurprised sigh*. // I feel like this is Mark's writing side showing through. "And how about I kill all of your favorite characters and cause more emotional trauma then necessary.